Brazil's rapid religious transformation is reverberating through the country's tight presidential race, where abortion and gay marriage have emerged as hot-button issues and Pentecostal televangelists could be political power brokers.

The socially conservative Pentecostal population now includes more than one-fifth of the electorate, just three decades after barely registering any presence at all. That change has the secular-minded incumbent quoting Psalms while her Bible-reading main rival has repeatedly stressed her belief in a secular state to avoid alienating liberal voters ahead of Sunday's first-round vote.

During a recent service at his 6,000-seat Assemblies of God church in a gritty Rio de Janeiro neighborhood, Brazil's most influential Pentecostal pastor spent half of the service talking about the election, nudging voters to support top opposition candidate Marina Silva, who is a member of the Assemblies of God, by far Brazil's largest Pentecostal denomination.

If Silva makes it to the second round and defeats incumbent Dilma Rousseff in an expected Oct. 26 runoff, she would become the first Pentecostal leader of a country with more Catholics than any other.

"A pastor isn't the owner of anybody's ballot. I don't have a band of angels who can peek over your shoulder in the voting booth," said Silas Malafaia, his face looming on two jumbo TV screens bookending the enormous stage where he paced. "But you've got to vote your conscience. Don't just give your vote away. Vote against the corrupt and those who want to destroy the family!"

Malafaia alone has 800,000 followers on Twitter, books that have sold in the millions and sermons beamed around the globe. He is part of a rapidly swelling movement that is strongly rooted among poorer Brazilians, a group that otherwise heavily favors Rousseff's Workers Party, which has lifted millions from poverty with expansive social welfare programs and the creation of millions of new jobs.

In a survey released Friday, the Datafolha polling group found that 54 percent of Pentecostal voters would support Silva in an expected second-round vote, while Rousseff was favored by 38 percent. Among the population as a whole, the two were neck and neck. Datafolha polled 11,474 people across Brazil on Sept. 25-26 and the margin of error was two percentage points.

But in a Datafolha poll released Tuesday night, Rousseff had pulled ahead of Silva in a second-round vote, leading 49-to-41. A breakdown by religion in the latest poll was not yet available.

Rousseff, a former Marxist guerrilla who was imprisoned and tortured during Brazil's military dictatorship, rarely spoke of religion before this campaign, but she has been making the rounds of Pentecostal churches and invoking God's name of late.

In August she spoke to hundreds of Pentecostals in Sao Paulo at an Assemblies of God church.

"I'm opening my remarks by saying that the Brazilian state is secular," Rousseff said to a silent crowd.

"But, citing the Psalm of David, I'd like to say that 'Joyful is the nation whose God is the Lord,'" she immediately added, to loud applause.

By contrast, the deeply religious Silva has made no campaign stops in churches and has kept Pentecostal leaders at arm's length in public, hoping to combat suspicions among non-religious voters that conservative pastors could shape the stance a Silva government would have on social issues.

Those worries intensified when her official platform reversed support for gay marriage less than 24 hours after its release last month, following blistering attacks on the proposal from Malafaia and other Pentecostal leaders. Silva supports Brazil's current law allowing same-sex civil unions, which gives gay partners the same rights as heterosexual couples, but stops short of supporting religious weddings for gays.

As an impoverished daughter of a rubber tapper deep in the Amazon, Silva wanted to become a nun and as a teenager moved into a convent, where she first learned to read and write at age 16. There, she came into contact with priests adhering to liberation theology, a Latin American-inspired movement that advocates for the poor.

But in 1997, facing extreme health problems after five bouts with malaria as a girl and hepatitis as a teenager, Silva, then a senator, converted to the Pentecostal faith upon being told by a doctor that only a miracle could help her.

For some, Silva's mixed religious background could be a political asset.

"Marina is in a really nice position where she got Malafaia, the rock star pastor of the Assembly of God, to back her, so she probably feels like a lot of her evangelical support is solidified," said Andrew Chesnut, a professor and expert on Latin American religions at Virginia Commonwealth University, who has focused on Brazil's Pentecostals. "And the fact she was involved with liberationist Catholicism ... means more progressive Catholics will sympathize with her."

But when it comes time to cast their ballot, Brazilian Pentecostals, who are overwhelmingly poor, will face a dilemma in choosing between Silva, a woman who shares their faith, and their gratitude to Rousseff's Workers Party for strong socio-economic advances in the last 12 years.

Michelle Jeronimo, a 22-year-old heading into Malafaia's service last week, said Silva would get the backing of Pentecostals because she would maintain "God's posture" in the face of widely perceived government dishonesty.

"Pentecostals are so disappointed with the corruption, with the broken promises, so they're looking to this Pentecostal side of her," Jeronimo said, adding that Silva will "fulfill what she said, what she promised, what she said she intends to do."

But Silre Noguiera, handing out campaign fliers for Pentecostal congressional candidates outside Malafaia's church, looked over her shoulders before whispering where her political allegiance lay.

"The Workers Party governments are the only ones that ever did anything for the poor. Dilma has my vote," she said. "I'm not convinced most Pentecostals will vote based on religion. At the end of the day, they want a president who'll give them a better life."

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Brad Brooks on Twitter: www.twitter.com/bradleybrooks